Resistance and friction from air surrounding one or more moving components (for e.g., a transmission with high speed gears, a crankcase, etc.) of a vehicle's propulsion system can contribute to fuel efficiency losses and system degradation. These losses may be most pronounced within a crankcase of a vehicle which may be turbulent particularly at high engine speeds. Further, air surrounding the crankshaft may contain suspended oil droplets which can increase drag forces due to an increase in density, thereby increasing engine load and decreasing fuel economy.
In the power generation industry, friction from air surrounding high speed electrical machinery may be reduced by flooding the machinery with hydrogen gas, which has a lower viscosity than air. However, hydrogen gas may be easily ignited.
Since air resistance is proportional to the density of the air surrounding rotating components, friction losses may also be reduced by decreasing this density. Density may be decreased by decreasing the amount of air within the case or enclosure containing the rotating system by creating a vacuum within the system. However, since air flow over the rotating components provides cooling effects to reduce degradation from overheating, eliminating or reducing the volume of air coming into contact with the rotating components can have negative effects on the machinery.
The inventors herein have recognized the above issues and identified an approach to at least partly address the issues. One example approach that at least partially addresses the above issues and that can achieve the technical result of reducing friction in an internal combustion engine is to fill or partially fill the engine transmission and crankcase with a gaseous fuel such as methane. For example, the inventors have realized that by replacing at least some of the air within the engine crankcase with a lower density gas, suspended oil droplets may impinge more easily to form fewer larger drops thus reducing the effective air density within the crankcase. Therefore, air resistance can be decreased while providing sufficient engine cooling. Furthermore, the viscosity of methane is substantially lower than air and the flammability of methane in air is limited.
Thus, in one embodiment, a vehicle system comprises an internal combustion engine including a positive crankcase ventilation (PCV) system, a gaseous fuel source and a transmission wherein the gaseous fuel source is fluidly coupled to the transmission via a flow control valve and the transmission is fluidly coupled to a fresh air line of the PCV system. The flow control valve is configured to control the flow of gaseous fuel into the transmission case. In this way, an existing source can supply gaseous fuel into the transmission case and thereafter, into the crankcase via the PCV fresh air line to reduce friction within both cases. By introducing the gaseous fuel into the crankcase via the PCV fresh air line, its flow may be advantageously utilized to carry blow-by gases into the intake manifold via the PCV valve.
In another embodiment, during a first condition, a method comprises delivering gaseous fuel from a gaseous fuel source to a transmission, and subsequently, a PCV system of an internal combustion engine, wherein the first condition comprises a calculated blow-by flow rate being less than a PCV valve flow rate. In this way, a gaseous fuel may be delivered into a transmission and a crankcase based on an existing PCV valve flow rate. By ensuring that gaseous fuel is drawn into the cases when a modeled blow-by flow rate is less than the PCV valve flow rate, an excess flow of gaseous fuel may be prevented. Additionally, an undue increase in crankcase pressure may also be avoided. Further, by controlling the flow of gaseous fuel based on an estimated blow-by flow, a desired air-fuel ratio may be maintained while reducing friction in the transmission and crankcase.
In a further embodiment, a vehicle may comprise a gaseous fuel source, an internal combustion engine including a PCV system and a transmission, wherein the gaseous fuel source is fluidly coupled to the transmission via a flow control valve, the flow control valve configured to control the flow of gaseous fuel into the transmission, and a controller having executable instructions to during a first condition, deliver gaseous fuel from a gaseous fuel source to the transmission and subsequently the PCV system of an internal combustion engine, wherein the first condition comprises a calculated blow-by flow rate being less than a PCV valve flow rate and a manifold vacuum being greater than a crankcase vacuum, wherein a flow rate of the gaseous fuel is calculated from a difference between a PCV valve flow rate and a blow-by gas flow rate, wherein the blow-by gas flow rate is calculated based on engine operating conditions.
In this way, aerodynamic friction losses experienced within a transmission and a crankcase may be diminished by partially filling each of the cases with a low density gas. An existing gaseous fuel source within a vehicle may be utilized for this purpose thus enabling cost and space savings. By flowing the gas when a modeled blow-by rate is less than a PCV valve flow rate, the fuel flow may compensate for the existing difference in flow rates. Further, by flowing the low density gas under conditions where the manifold vacuum is greater than crankcase vacuum, the gaseous fuel may be drawn easily along with blow-by gases into the manifold. Overall, benefits in fuel economy may be achieved.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.